Endurance, runway-dependency and the need for additional infrastructure for take-off and landing are among the most important characteristics of UAVs. Conventionally unmanned aerial vehicles can be divided into three classes, namely: i) high-endurance, runway-dependent aircraft, such as, e.g. Global Hawk; ii) high-endurance runway independent aircraft that need additional infrastructure for take-off and landing, such as, e.g. Boeing Scan Eagle; and iii) low endurance, runway independent aircraft that do not need any additional infrastructure for take-off and landing because of the capability to hover, such as any rotary wing aircraft, e.g. Boeing Unmanned Little Bird.
Typically, rotary wing aircraft have far lower aerodynamic efficiency and, therefore, range and endurance, than fixed wing aircraft. Lower aerodynamic efficiency is detrimental also to such parameters as speed and payload.
One use of UAVs is the inspection of power lines which stretch many hundreds of kilometres. Recently helicopter based UAVs have been used for power line inspection as fixed wing based UAVs do not have the capability to fly slow enough to perform detailed spot inspection, such as for hot-spots. Fixed wing UAVs also require infrastructure, such as runways, for take-off and landing. However, the helicopter based UAVs have far inferior endurance and range, as compared with fixed wing aircraft. This is due to an inherently lower efficiency of a rotor in forward flight, as compared with a fixed wing.
Hence, there is a need for high-endurance UAVs that can cover large distances while also able to hover and perform short/vertical take offs and landings. Such a UAV would also allow larger sections of power line to be inspected from a single launch site.